As part of the provincial Timber Supply Review, the B.C. Forest Service has examined the availability of timber in the Lillooet Timber Supply Area (TSA). The analysis assesses how current forest management practices affect the supply of wood available for harvesting over the next 200 years. It also examines the potential changes in timber supply stemming from uncertainties about forest growth and management actions. It is important to note that the various harvest forecasts included in the report only indicate the timber supply implications of current practices and uncertainty. As such, the forecasts should be used for discussion purposes only; they are not AAC recommendations.
The Lillooet TSA covers a total area of 1 124 000 hectares, of which about 304 600 hectares are considered available for timber harvesting under current management practices. Total volume of standing timber in the area is about 49 million cubic metres, of which 47 million cubic metres is of merchantable age. The area is dominated by spruce, Douglas-fir and lodgepole pine stands. The current allowable annual cut (AAC) for the Lillooet TSA is 650 000 cubic metres.
Current forest management of the Lillooet TSA includes recognizing areas with significant forest resource values such as aesthetics, wildlife and community water supply. These values have been accounted for by excluding some sensitive areas and applying forest cover requirements to the land base that is assumed to be available for timber harvesting.
Given current management assumptions, the analysis shows the current AAC can be maintained for another 30 years without causing a reduction in future harvest levels below the long-term level. After 30 years the harvest begins to decline at 8% each decade until the long-term level is reached in the ninth decade. The long-term harvest level, which is the potential maximum that can be harvested in perpetuity, is 400 000 cubic metres per year.
If there is no limit on how quickly future harvest levels decline and harvests are allowed to fall below the long-term level, then the current AAC can be maintained for 70 years. However, this would cause a serious timber shortage after 70 years that would last for many decades. If the harvest level were to be reduced immediately and maintained at the reduced level for as long as possible, then the existing growing stock would last longer and forests in the future would be older, on average. The magnitude of these effects depends on how much harvest levels are reduced. Reducing the harvest level may result in increased diversity in forest ecosystems in the future. On the other hand, the risk of timber losses to fire, insects and disease would increase.
Many of the data and assumptions used in the analysis are subject to varying degrees of uncertainty. As an example, Lillooet Forest District staff feel that the extent of the land base assumed available for timber harvesting is particularly uncertain. Sensitivity analysis was used to examine how uncertainty about data and assumptions affect the results of the timber supply analysis.
Over the first 8 to 10 decades, harvest levels
are most sensitive to a decrease in the amount of mature forest
available for harvesting, tightening of forest cover requirements
to account for non-timber values and changes to volume estimates
for existing timber. Short-term harvest levels are also moderately
sensitive to changes in minimum harvest ages and a requirement
to maintain old-growth stands. Harvest levels over that period
are not sensitive to yield estimates applied to future regenerated
stands. The long-term harvest level is sensitive to uncertainty
about regenerated stand yields and the land base assumed available
for harvesting. But in general, the long-term harvest level is
not very sensitive to uncertainty about other data and assumptions.